the loweft of which entered the earth to the depth of about three feet, in a perpendicular direction. The principal effects of the explosion were thefe: the brafs-pointed wires at the top of the apparatus, which were elevated only fix or feven inches above the chimney, were diffipated or melted: the rods were unhooked, and fome iron ftaples ftarted, by which they were held to the chimney; nevertheless they conducted the lightning without any injury to themselves, except that the infide of each hook was fuperficially melted; and without any damage to the chimney, till the lightning arrived at the foundation of it, which was fhattered almoft quite round, where feveral bricks were likewise torn out. On one fide it plowed up feveral furrows in the earth fome yards in length, tore up the hearth in feveral places, and did fome flight mifchief in the neighbourhood of the fireplace.

The deficiencies in the apparatus, indicated by these pheno mena were, first, that the pointed wires were not fufficiently elevated above the chimney, to prevent a ftroke, or to draw off the electric fluid filently, or without an explosion. To have a chance of anfwering this intention, which, (if we may judge from our experiments made on a smaller fcale) may in fome inftances be effected, they ought to have reached five or fix feet above the highest part of the building. The fecond defect was that, the rods being bent round into hooks, the space of contact between their extremities was fo fmall, that the large torrent of electrical matter, confined in thefe narrow ftraits, melted the metal, and, as generally happens in fuch cafes, partly exploded it; and, by this violent action of the electric matter, or perhaps merely by its repulfive power, the rods were unhooked or feparated from each other; nevertheless they performed their function of conducting this immenfe quantity of the electric fluid (which must probably have rent fo imperfect a conductor as the chimney itself from top to bottom) with perfect fafety to the whole building, till the lightning arrived at the extremity of the rod near the foundation. And here we find the principal defect of this apparatus. The rod not being carried to a fufficient diftance from the foundation, nor low enough to arrive at water, or a fufficient quantity of moift earth, the electric fluid, accumulated near its lower end, quitted the rod near the furface of the earth, and, dividing itfelf in fearch of other paffages, produced the effects above-mentioned. On the whole, the Author, on very good grounds, concludes, that the houfe and its inhabitants were faved by the rod, and that, if it had been made of one piece, and had been funk deeper in the earth, or had entered the earth at a greater diftance from the foundation, the mentioned fmall damages (except the melting of the points) would not have happened,' .

In

In letter 60th, the Author takes proper notice of the inconfequential manner in which the Abbé Nollet reasons against the utility of metalline conductors, in his paper on that fubject, published in the Memoirs of the Royal Academy of Sciences for the year 1764. The Abbé cautions people not to depend fo far on the benediction which has been bestowed on church bells as to ring them during a thunder ftorm, leaft the lightning, in its way to the earth, fhould be conducted down to them by the bell ropes, which, as the Author obferves, are but bad conductors; and yet is against fixing metal rods on the outfide of the fteeple, which are known to be much better conductors, and which it would certainly choose to pass in, rather than in dry hemp.' The Reader may find fome ftrictures of our own on this Memoir, by turning to our Appendix to the 38th vol. p. 575. On this occafion the Author obferves that it appears, during a courfe of more than 12 years experience, that among the great number of houfes furnished with iron rods in America, feveral have been evidently preferved by their means; while a number of houfes, churches, barns, fhips, &c. in different places, unprovided with rods, have been ftruck and greatly damaged, demolished, or burnt :'-and further, that, in all the inftances yet known of houfes ftruck by lightning, which have been provided with rods, the lightning has confiantly pitched down upon the point of the rod, and has never attacked any other part of the building.

This letter of the Author's is introduced by the following extract from a letter of J. Winthrop, Efq; profeffor of natural philofophy at Cambridge, in New-England, dated January 6, 1768, which we recommend to the perufal of the inhabitants of St. Bride's, London.

I have read, fays the profeffor, in the Philofophical Tranfactions, the account of the effects of lightning on St. Bride's fteeple. 'Tis amazing to me that, after the full demonftration you had given of the identity of lightning and of electricity, and the power of metalline conductors, they fhould ever think of repairing thar fteeple without fuch conductors. How aftonifhing is the force of prejudice, even in an age of fo much knowledge and free enquiry!'

Philofophy, we fear, in vain lifts up her ftill and gentle voice, and unavailingly calls out across the Atlantic, at this time, to these inhabitants of the patriotic ward of Farringdon Without.-Deaf to the voice of the charmer, charm she never fo wifely, thefe watchful guardians and fupporters of the rights of a great nation are at préfent, we apprehend, too much occupied to liften to the fmall concerns of their parish, or to attend to the well being of a fteeple. In our review of Dr. Pricftley's Hiftory of Electricity, animated with a defire of guarding

We

guarding this beautiful ftructure from that deftruction with which, either from its fituation, or from other causes, it seems to be peculiarly threatened, we conveyed to their notice, and endeavoured to fecond, the ingenious Author's tacit and gentle reproof on this fubject; and afterwards [Appendix to 38th vol. p. 576.] briefly ftated, in general, the propriety of providing a paffage for the thunderbolt, through those media which it most affects. The tremendous activity of this matter can only be counteracted or evaded, on two principles; that of refifting its paffage by non-conductors, or of giving way to it, by providing proper fubftances to conduct it to the earth. Now as churches and houses cannot be conftructed of glafs or amber, but of ftones and mortar, and other imperfeally refifling materials, fecurity against its ravages can only be obtained by adopting the principle of non-refiftance, in the moft unlimited extent. beg pardon of thete patriotic fpirits for inculcating fuch feemingly flavish doctrines; but we beg leave to remind them that patriots and placemen fhould equally fubmit, with a good grace, to phyfical neceffity. We would appeal even to their dauntless alderman himself, who has fo ftrenuously refifted the thunderbolts of minifterial power, whether they ought not to yield the most implicit paffive obedience to this celeftial meffenger; who, though he comes armed with all the terrors of a general warrant, will execute it peaceably and inoffenfively if he meets with no refiftance.-To lay afide all metaphor and allufion, and to speak to the comprehenfion of every inhabitant who pays fcot and lot in the parish of St. Bride's [for tho' all of them undoubtedly, to a man, are politicians, they may not all be philofophers and electricians] we would recommend to their confideration whether, as they provide fpouts to convey away the rain which falls upon their church, they fhould not provide a channel likewife to carry off the electricity. And when the goodly fabric of the British conftitution (which, they tell us, is become crazy all on a fudden) fhall, through the care of these ever-attentive, and now particularly apprehenfrue citizens, have undergone a thorough reparation, we hope they will caft an eye towards the grievous ftate of their defenceless fteeple.

That we may leave nothing effential relating to this fubject unnoticed, we fhall obferve, that although no reasonable doubt. can now be entertained with regard to the power here afcribed to metalline conductors, yet a kind of fchifin has arifen among electricians concerning the best form of construction of the upper part of the apparatus: fome recommending its terminating in a knob inftead of a point, on a fuppofition that the points invite the ftroke. It is true, the Author obferves, that points draw electricity at greater diftances in the gradual filent way' (which is, in fact, one of their advantages) but knobs will

5

draw,

draw, at the greatest distance, a ftroke.' He proves this by an eafy and conclufive experiment made with a charged Leyden vial, the wire of which will not frike into a pointed body, connected with its outfide, unless the latter be brought much nearer to it, than a knob requires to be, to produce the fame effect. Points likewife, he obferves, tend to repel the fragments of an electrified cloud; while knobs actually invite, or draw them nearer; as the Author long ago proved by an ingenious experiment made with an electrified fleece of cotton, representing a cloud; which was repelled, or driven upwards on presenting a pointed body underneath it, and attracted downwards, on the approach of a blunt body.

In the 32d letter, the Author gives an account of an experiment made with the late Dr. Hadley of Cambridge, on the cold produced by evaporation, in which the effects were greater than any which we have yet feen defcribed. The ball of a thermometer was repeatedly and alternately wetted with Ether, and blown upon with a bellows to quicken the evaporation; by which means the included liquor defcended from fixty-five degrees, the heat of the air at that time, down to feven; that is, twenty-five degrees below the freezing-point; its bulb, at the end of the experiment, being covered near one-fourth of an inch thick with ice, proceeding either from water mixed with the Ether, or from the breath of the affiftants.

From hence the Author infers the poffibility even of freezing a man to death on a warm fummer's day, if he were to stand in a paffage through which the wind blew brifkly, and were to be frequently wetted with this inflammable fpirit. At least, there is little room to doubt, that it is in confequence of this frigorific property of evaporating fluids, that the tender leaves of plants are, by their increafed tranfpiration, kept cool, and protected from the fcorching rays of the fun; and that, from this caufe, the heat of the human body rifes very little higher in the hottest climates, (where the fun raises the thermometer feveral degrees above that of the blood) than in the more temporate or even cold ones. The Author gives an inftance, in his own person, of the coolness produced by fweating, or animal evaporation in the human body, when breathing an air, or furrounded by bodies, hotter than itself; from whence it may be concluded, that the body of a dead man, expofed to these exceffive heats, would be hotter than that of a living man; though, on account of the moisture contained in it, there can be little doubt that it would be cooler than the dry earth expofed to the fame heat.

This fingular property of evaporating fluids, though only lately taken notice of by philofophers, has long, as the Author obferves, been usefully applied in the east, to the cooling of water,

(when

(when carried on the backs of camels travelling over the dry defarts in that hot climate) by means of wet woollen cloths wrapped round the flafks containing it. A curious inftance is likewife given, which fhews, that our common failors had fome notion of this property, or at least applied it to use. Being at fea, when a youth, the Author obferved one of them, during a calm in the night, often wetting his finger in his mouth, and then holding it up in the air, to difcover, as he faid, if the air had any motion, and from which fide it came; and this he expected to do, by finding one fide of his finger grow fuddenly cold,' (evidently from the increafed evaporation caufed by the otherwife imperceptible breath of air blowing on that fide,) and from that quarter he fhould look for the next wind.-Natural knowledge might undoubtedly be confiderably enriched, if philofophers would oftener condescend to attend to feveral simple phanomena, and popular practices and obfervations, by which the fecret operations of nature may fometimes be as fuccessfully detected, as by the more complex and operofe experiments of the philofopher. Had an electrician, for inftance, lived in the neighbourhood of the caftle of Duino *, where from time immemorial it has been customary to draw fparks from a pike planted on the baftions, on the approach of a thunder ftorm, he might, though poffeffed of a very small portion of our Author's fagacity, have anticipated him in his great and important difcovery of the identity of lightning and the electric matter. Many fimilar inftances might be produced.

We fhall close this article for the prefent, by an account of a philofophical inftrument, which the Author met with in Germany; the fingular phænomena of which may amufe the curious, and afford matter for fpeculation to the philofopher. It confifts of a glafs tube, about eight inches long, having a hollow ball of near an inch diameter at one end, and one of an inch and half at the other, hermetically fealed, and half filled with water. If the smaller ball be held in the hand, and the other be a little elevated above the level, a conftant fucceffion of large bubbles is feen proceeding from the lower ball to the upper. Mr. Nairne, an ingenious artift here,' adds the Author, has made a number of them from mine, and improved them; for his are much more fenfible than those I brought from Germany +. I bored a very fmall hole through the wainscot in the feat of my window, thro' which a little cold air conftantly entered, while the air in the room was kept warmer by fires daily made in it, being winter time. I placed one of his glaffes, with the eleva

See Appendix to the Monthly Review, vol. xxxviii. + In Mr. Nairne's improved inftrument, the connecting tube is much fmaller, and the balls larger, and are turned up at right angles to it.

ted